To observe an interior structure of a minute area of an object, a scanning transmission electron microscope (STEM), a transmission electron microscope (TEM), or the like is used. As a typical method of observing an interior of a sample using such an electron microscope, arranging the sample sliced thinly to be able to transmit an electron beam, on a mesh-like sample table including a large number of holes, and acquiring a transmitted electron beam by a detector arranged at an opposite side to an electron source side with respect to a sample surface is known. However, in this method, the sample floats on the holes of the mesh, and thus work to mount the sample on the sample table is extremely difficult. Therefore, PTL 1 has proposed an electron detector that allows an observation sample to be directly placed.
Further, the minute area of an object can be observed only by the electron microscope but also by an optical microscope. By use of the optical microscope, color information, which cannot be acquired by the electron microscope in principle, can be acquired. The optical microscope can acquire a transmitted optical image by irradiating the sample with white light or specific light and focusing light having the color information absorbed in the sample or emitted from the sample. Accordingly, for example, by putting a specific dyeing material into a biological cell sample, only a specific area in a cell can be dyed. Therefore, which area is dyed or not dyed can be observed by observing the color. Especially, the optical microscope is widely used in pathological diagnosis or in the field of life science.
While the electron microscope cannot acquire the color information, the electron microscope can observe the minute area with high resolution, which cannot be observed by the optical microscope. Further, information obtained from the electron microscopic image is information that reflects a difference in density of the sample, and is different from information obtained by the optical microscope.